[rules-users] Human Task - ERROR : JPAKnowledgeService.newStatefulKnowledgeSession ...

Hello all, I get an exception while last line of below method executed :     public StatefulKnowledgeSession createSession() throws Exception {                 /*          * Create the knowledgebase using the required bpmn and drl files          */         KnowledgeBase kbase = readKnowledgeBase("HumanTask.bpmn");         EntityManagerFactory emf = Persistence.createEntityManagerFactory( "org.jbpm.persistence.jpa" );         Environment env = KnowledgeBaseFactory.newEnvironment();         env.set( EnvironmentName.ENTITY_MANAGER_FACTORY, emf );         env.set( EnvironmentName.TRANSACTION_MANAGER, TransactionManagerServices.getTransactionManager() );         env.set( EnvironmentName.GLOBALS, new MapGlobalResolver() );                 Properties properties = new Properties();         properties.put("drools.processInstanceManagerFactory", "org.jbpm.persistence.processinstance.JPAProcessInstanceManagerFactory");         properties.put("drools.processSignalManagerFactory", "org.jbpm.persistence.processinstance.JPASignalManagerFactory");         KnowledgeSessionConfiguration config = KnowledgeBaseFactory.newKnowledgeSessionConfiguration(properties);             return JPAKnowledgeService.newStatefulKnowledgeSession(kbase, config, env);                 }   its stack-trace is : 14:26:13,111 WARN  [JtaTransactionManager] Participating in existing JTA transaction, but no JTA TransactionManager or TransactionSychronizationRegistry available: java.lang.NullPointerException     at org.drools.persistence.jta.JtaTransactionManager.registerTransactionSynchronization(JtaTransactionManager.java:221)     at org.drools.persistence.SingleSessionCommandService.registerRollbackSync(SingleSessionCommandService.java:333)     at org.drools.persistence.SingleSessionCommandService.<init>(SingleSessionCommandService.java:123)     at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)... Can anyone help me to solve this problem ? Thanks in advance S.M.H.Jamali